Multi-frequency local oscillators

ABSTRACT

A multiple-frequency local oscillator for providing an LO signal at one of a multiple of predetermined resonant frequencies associated with a number of resonators is disclosed. It includes a number of LO input ports for coupling to a plurality of resonators, respectively, each resonator having a predetermined resonant frequency; the local oscillator is controlled to selectively provide at its LO output port an output LO signal at any one of the resonant frequencies.

FIELD OF THE INVENTION

The present invention relates to local oscillators and moreparticularly, local oscillators for selectively providing oscillationsignal at one of a multiple of predetermined frequencies.

BACKGROUND OF THE INVENTION

Frequency downconverters are commonly used in cable TV ("CATV") anddirect broadcast satellite ("DBS") systems for converting a receivedradio-frequency ("RF") signal into an intermediate frequency ("IF")signal.

A frequency downconverter system generally includes three basicfunctional blocks: a low noise RF amplifier ("LNA") for amplifying areceived RF signal, a local oscillator ("LO") for providing an LOsignal, and a mixer for combining the amplified RF signal and the LOsignal to generate an IF signal.

In the currently used European DBS systems, the input RF signalfrequency is between 10.7 and 11.8 GHz, which is downconverted to an IFsignal frequency between 950 and 2050 MHz; the LO signal frequency usedis about 9.7 GHz.

To expand the number of channels that can be provided by the DBSsystems, it has been proposed to increase the input RF signal frequencyspectrum from 10.7-11.8 GHz to 10.7-12.75 GHz to cover two frequencybands, 10.7-11.7 GHz and 11.7-12.75 GHz. The IF signals corresponding tothe two RF bands will have frequencies of 950-1950 MHz and 1100-2150MHz, respectively. The LO frequencies required for the two RF bands willbe 9.75 GHz and 10.6 GHz, respectively.

One approach for providing a DBS reception system capable of operatingat both RF bands is illustrated in FIG. 1. In this approach, adownconverter system 100 consists of an antenna 105 for receiving an RFsignal from a satellite and an LNA 110 connected to the antenna foramplifying the received RF signal. The amplified RF signal is thendivided into two routes, one to a 10.7-11.7 GHz band pass filter 115followed by a downconverter 120 operating with an LO signal of 9.75 GHz,and the other to an 11.7-12.75 GHz band pass filter 125 followed byanother downconverter 130 operating with an LO signal of 10.6 GHz. Atthe output of downconverter 120, an IF signal between 950-1950 MHz isprovided, whereas at the output of downconverter 130, an IF signalbetween 1000-2100 MHz is provided. Consequently, this system covers bothRF frequency bands, i.e, 10.7-11.7 GHz and 11.7-12.75 GHz.

One major drawback associated with the above-described system is that itrequires two independent downconverters, thus making it more expensivethan the currently used single downconverter system operating at asingle LO frequency of 9.7 GHz. A single downconverter capable ofoperating at both RF bands is desired, which requires a local oscillatorcapable of selectively providing an LO signal at either 9.75 GHz or 10.6GHz.

It is therefore an object of the present invention to provide an LOwhich can selectively provide an LO signal at one of a multiple ofpredetermined frequencies;

it is another object of the present invention to provide means forcontrolling the LO to select one of the predetermined multiple LOfrequencies;

it is further an object of the present invention to provide an LO forselectively providing an LO signal at either 9.75 GHz or 10.6 GHz; and

it is yet another object of the present invention to provide a frequencyconverting device including a multiple-frequency local oscillator.

SUMMARY OF THE INVENTION

Those and other objects and advantages are achieved in the presentinvention, which provides a multiple-frequency local oscillator and afrequency converting device utilizing the multiple-frequency localoscillator.

The multi-frequency local oscillator of the present invention includes anumber of input ports coupled to a number of external resonators,respectively, each having a predetermined resonant frequency, an LOoutput port, and means for controlling the oscillator to selectivelyprovide an LO output signal at any one of the resonant frequencies atthe LO output port.

In one embodiment, a multiple-frequency LO includes a plurality ofoscillator circuits, each having its input terminal connected to an LOinput ports for coupling to a resonator; the output terminals of theoscillation circuits are connected together to an LO output port. Themulti-frequency local oscillator further includes means for controllingthe plurality of oscillator circuits such that only one of them isselected to operate while the other ones are prevented from operation.Consequently, by selecting the oscillator that is coupled to theresonator having the desired resonant frequency, this local oscillatorprovides at the LO output port an output LO signal at the desiredfrequency.

In a preferred embodiment, the multi-frequency local oscillator is inthe form of a GaAs monolithic integrated circuit and comprises twodepletion mode GaAs FETs. The gate terminals of the GaAs FETs areconnected to two LO input ports for coupling to two external dielectricresonators, respectively, having resonant frequencies of 9.75 GHz and10.6 GHz. The source terminals of the two GaAs FETs are connectedtogether and then coupled to the ground through a common sourceimpedance circuit. The drain terminals of the GaAs FETs are coupled to aDC power supply through two inductors, respectively, and a commoninductor. At the intersection of the two inductors and the commoninductor, an output LO signal is provided.

When operating, the output LO frequency is selected by applying a groundor a positive potential to the FET gate terminal that is connected tothe resonator having the desired resonant frequency so as to turn on theFET, while applying a negative potential to the gate terminal of theother FET to turn it off. As a result, the selected FET operates inconjunction with the resonator connected thereto to provide an LO signalat the resonant frequency of the resonator.

In another embodiment, a multiple-frequency local oscillator includes anoscillator circuit and a switching circuit. The oscillator circuit hasan output node connected to an LO output port and an input nodeconnected to an output node of the switch circuit. The switching circuithas a plurality of input nodes connected to a plurality LO input ports,respectively, for coupling to a plurality of external resonators.

When operating, the switching circuit is controlled such that it couplesonly one resonator to the oscillator circuit while it decouples all theother resonators from the oscillator circuit. As a result, the localoscillator provides an output LO signal at a frequency that is theresonant frequency of the one resonator coupled to the oscillatorcircuit. By selectively coupling the desired resonator to the oscillatorcircuit, this multi-frequency local oscillator provides an LO signal atany one of the resonant frequencies of the resonators.

In a preferred embodiment, this multi-frequency local oscillator is aGaAs monolithic IC which is defined by two functional circuit blocks, anoscillator circuit and a switching circuit. The former includes adepletion mode GaAs FET, the drain terminal of which is coupled to a DCpower supply through a drain impedance load, and the source terminal ofwhich is coupled to the ground potential via a source impedance. Theintersection of the drain terminal and its impedance load is connectedto an LO output port of this local oscillator.

The switching circuit is mainly composed of two depletion mode GaAsFETs, each having its drain terminal connected to the gate terminal ofthe FET in the oscillator circuit. The source terminals of the FETs arecoupled to two external dielectric resonators, respectively; theresonators have respective resonant frequencies of 9.75 GHz and 10.6GHz. By applying appropriate voltages to the gate terminals of the twoFETs, respectively, so as to allow the desired resonator to couple tothe oscillator circuit while to decouple the other resonator, thefrequency of the output LO signal is thus selected to be the resonantfrequency of the resonator coupled to the oscillator circuit.

The present invention is also directed to frequency conversion devicessuch as upconverters or downconverters utilizing the multi-frequencylocal oscillators of the present invention. specifically, a frequencyconversion device of the present invention comprise two basic functionalblocks, a mixer circuit coupled to a multi-frequency local oscillator.When operating, the mixer circuit receives an RF signal, combines itwith an LO signal received from the multi-frequency local oscillator,and provides an output IF signal. The LO signal frequency is one of amultiple of frequencies and is selected to suit a particular input RFfrequency range.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, features and advantages of the presentinvention will be more apparent from the following detailed descriptionin conjunction with the appended drawings in which:

FIG. 1 illustrates a prior art frequency converting system;

FIG. 2 depicts a multiple-frequency local oscillator of the presentinvention;

FIG. 3 depicts a first embodiment of the multiple-frequency localoscillator of the present invention;

FIG. 4A is a schematic circuit diagram of a preferred embodiment of thefirst embodiment;

FIG. 4B shows the schematic circuit diagram of an alternative embodimentto the circuit of FIG. 4A;

FIG. 5 illustrates another preferred embodiment of the first embodiment;

FIG. 6 depicts another alternative embodiment of the present invention;

FIG. 7 is a schematic circuit diagram of another embodiment;

FIG. 8 illustrates a second embodiment of the present invention;

FIG. 9 shows the schematic circuit diagram of a preferred embodiment;

FIG. 10 depicts a preferred embodiment of a frequency conversion deviceof the present invention; and

FIG. 11 illustrates another preferred embodiment of a frequencyconversion device of the present invention.

DETAILED DESCRIPTION

The present invention is directed to a multi-frequency local oscillatorand to the application of the multi-frequency local oscillator to afrequency conversion device such as an upconverter or a downconverter.

Referring to FIG. 2, a multiple-frequency LO 200 of the presentinvention has a number of input ports 205 for coupling to a number ofexternal resonators 210, respectively, and an output port 215. Each ofthe external resonators has a distinct resonant frequency, f_(i).Multi-frequency LO 200 operates with resonators 210 to selectivelyprovide at output port 215 an output signal at any one of the resonantfrequencies.

In a first embodiment of the present invention, illustrated in FIG. 3, amulti-frequency local oscillator 300 includes a number of oscillatorcircuits 320. Each oscillator circuit 320 has an input terminal 325connected to an LO input port 305 for coupling to a resonator 310, andan output terminal 330 connected to an LO output port 315. Eachoscillator circuit is capable of operating in conjunction with theexternal resonator connected thereto to generate at output port 315 anLO signal at the resonator's resonant frequency.

The local oscillator further provides means for controlling oscillatorcircuits 320 such that only one of them is selected to operate while theothers are prevented from operation. As a result, the operating oneoscillator circuit operates in conjunction with the resonator connectedthereto to provide at output port 315 an LO signal at the resonantfrequency of the resonator.

A preferred embodiment, illustrated in FIG. 4A, provides a localoscillator 400 in the form of a GaAs monolithic integrated circuit (IC)and it includes two depletion mode GaAs Field Effect Transistors("FETs") 425 and 430.

The gate terminal of FET 425 is connected via an input port 405 to anexternal dielectric resonator 410 having a resonant frequency of 9.75GHz. The gate terminal of FET 430 is connected to another externaldielectric resonator 420 having a resonant frequency of 10.6 GHz.

The source terminals of FETs 425 and 430 are connected together and arecoupled to the ground through a common source impedance circuit 435including inductor 440, capacitor 450 and resistor 445. The drainterminal of FET 425 is coupled to a DC supply V_(DD) through inductors455 and 465. The drain terminal of FET 460 is connected to V_(DD)through inductors 460 and 465. The output LO signal is provided at an LOoutput port 415.

The LO operates as follows: To provide an LO signal at 9.75 GHz, anegative DC potential sufficiently large to turn FET 430 off is appliedto the gate of FET 430 while the ground or a positive potential isapplied to FET 425 so as to turn it on. (In the context of the presentinvention and also well known to those skilled in the art, a FET is"turned on" when it is substantially conducting across the source anddrain terminals of the FET, and it is deemed to be "turned off" when itdisplays substantial resistance between its source and drain terminals).Because FET 430 is turned off, it will not operate with resonator 420 togenerate a 10.6 GHz signal. FET 425 is turned on and it operates inconjunction with resonator 410 to provide a 9.75 GHz LO signal at outputport 415.

To obtain an output LO signal at 10.6 GHz, a negative DC voltage isapplied to the gate terminal of FET 425 such that FET 425 is turned offand the ground or a positive potential is applied to FET 430 to turn iton. A 10.6 GHz LO signal is thus obtained at LO output port 415.

In this multi-frequency local oscillator, the DC voltages applied to thegate terminals of FETs 425 and 430 may be generated and provided by anysuitable circuit. One way to provide the DC voltages, as illustrated inFIG. 4B, is to utilize a control circuit 470 which receives a controlsignal 475 and provides DC signals 480 and 485 to the gate terminals ofFETs 425 and 430, respectively. In DBS or CATV systems, the controlsignal may be, for example, a signal for changing the TV channel.

It will be apparent to those skilled in the art that other means orcircuits may be used to provide voltages to the gates of the FETs aslong as desired voltages are provided to the FETs. The operation of themulti-frequency local oscillator of the present invention does notrequire any specific type of circuits to provide the gate controlvoltages.

It should be noted that the above-described preferred embodiment usesdepletion mode GaAs FETs as an example. As it is known to those skilledin the art, other types of transistors such as enhancement mode GaAsFETs, bipolar transistors, or silicon MOS transistors may also be usedin the LO in place of the GaAs FETs; they are all within the scope ofthe present invention.

It should also be noted that, although dielectric resonators are used inthe preferred embodiment, it is by no means a limitation to the presentinvention. As known to one skilled in the art, other types of resonatorssuch as varactor diodes and any other circuits that provides oscillationsignals at desired LO frequencies may be used in place of the dielectricresonators used in the preferred embodiment; they are also within thescope of the present invention.

The above-described preferred embodiment includes two GaAs FETs sharinga common source impedance load. Alternatively, each FET can have its ownsource load. As depicted in FIG. 5, the source load of FET 425 is acircuit including inductor 426, resistor 427 and capacitor 428, 30whereas the source load of transistor 430 includes inductor 431,resistor 432 and capacitor 433. This local oscillator offers theadvantage that the source load for each FET can be chosen independentlyfrom the source load of the other FET, thus offering more designfreedom.

In the above-described preferred LO, the GaAs FETs are coupled to theexternal resonators at their gate terminals. Alternatively, the externalresonators can also be coupled to the source terminals of the GaAs FETs.respectively, to generate LO signals.

Illustrated in FIG. 6, an LO 500 comprises two depletion mode GaAs FETs546 and 547, the source terminals of which are coupled to externalresonators 521 and 526, respectively, through input ports 520 and 525.The two FETs are turned on or off by control voltages V₁ and V₂ appliedto their gates, respectively, through ports 530 and 535. The LO providesan output LO signal at an LO output port 515. The output LO signalfrequency is selected by turning on the FET that is coupled to theresonator having the desired resonant frequency while keeping the otherFET turned off.

A major advantage of the LO of the present invention is that they can beeasily made to provide LO signals at any desired number of frequencies.As depicted in FIG. 7, an LO for providing a signal at one of 2Nfrequencies is obtained by parallel connecting 2N FETs, each having itsgate terminal connected to a resonator having a particular resonantfrequency. In GaAs circuit layout, a large GaAs FET (i.e., a GaAs FEThaving a large ratio of gate-width to gate-length) which is the kindnormally used in an LO, is usually formed by connecting, the drains,sources and gates, respectively, of a number of parallel located smallFETs. Using simple design modification such as breaking the connectinggates of the small FETs, the number of external resonators coupled tothe LO can be easily altered.

A second embodiment of the present invention, illustrated in FIG. 8,provides a multiple-frequency local oscillator 600 which includes anoscillator circuit 620 and a switch circuit 640. Oscillator circuit 620has an input node 630 connected to an output node 635 of the switchcircuit and an output node 625 connected to an LO output port 615.Switch circuit 640 has a number of input terminals 645 coupled to anumber of LO input ports 605 for coupling to a number of resonators 610,respectively.

When operating, the switch circuit is controlled to selectively coupleonly one of the resonators to the oscillator circuit while decouplingthe other resonators from the oscillator circuit. Consequently, at theLO output port, an LO output signal at the resonant frequency of theselected resonator is provided. By selecting the desired resonator tocouple to the oscillator circuit, the local oscillator can provide an LOsignal at any one of the resonant frequencies of the resonators.

Referring to FIG. 9, in a preferred embodiment, a local oscillator 700is in the form of a GaAs monolithic IC having two functional blocks, anoscillator circuit portion 720 and a switch portion 725. Oscillatorportion 720 includes a GaAs depletion mode FET 730 having its sourceterminal coupled to the ground potential via a circuit includinginductor 735, resistor 740 and capacitor 745, and its drain terminalcoupled to a DC power supply V_(DD) via two inductors 750 and 755. Theintersection between inductors 750 and 755 is connected to an LO outputport 715.

Switch circuit portion 725 includes two additional depletion mode GaAsFETs 760 and 765. The source terminals of FETs 760 and 765 arecapacitively coupled to two dielectric resonators 710 and 712,respectively, via LO input ports 705 and 706. The drain terminals of theFETs are connected to the gate terminal of FET 730 and are DC biased bythe DC power supply V_(DD) via two resistors 770 and 775. The gateterminals of FETs 760 and 765 are connected to LO input ports 705 and706 through resistors 780 and 785, respectively.

This local oscillator operates as follows: Suppose dielectric resonators710 and 712 have resonant frequencies of 9.75 GHz and 10.6 GHz,respectively. When a negative potential is applied to the gate of FET765 through port 706, FET 765 is turned off and resonator 712 isdecoupled from oscillator circuit portion 720. By applying the ground ora positive potential to the gate of FET 760 to turn it on, the 9.75 GHzresonator 710 is thus coupled to the gate of FET 730 through FET 760.The oscillation circuit portion operates in conjunction with resonator710 to provide a 9.75 GHz signal at the LO output port.

Alternatively, by applying appropriate potentials to the gate terminalsof FET 760 and 765 such that FET 760 is turned off and FET 765 is turnedon, an LO output signal at a frequency of 10.6 GHz results. Thepotentials to the gates may be applied from the resonators. As in thecase of the first embodiment, a control circuit or other type ofcircuits may be used to provide the potentials to the gate terminals ofFETs 760 and 765.

In accordance with the present invention, a frequency conversion deviceincluding a multi-frequency local oscillator is provided. The frequencyconversion device comprises a mixer circuit coupled to amultiple-frequency local oscillator for receiving an LO signal at one ofa number of predetermined LO frequencies. The mixer circuit receives aninput RF signal and combines it with the LO signal to generate an outputIF signal.

Referring to FIG. 10, in a preferred embodiment, a frequency conversiondevice 800 is in the form of a GaAs monolithic IC and it includes amixer circuit 805 coupled to an RF amplifier 810, an IF amplifier 820and a multiple-frequency local oscillator 815. Multi-frequency localoscillator 815 is coupled at its two LO input ports to two externaldielectric resonators 825 and 830 having resonant frequencies of 9.75GHz and 10.6 GHz, respectively. The local oscillator is controlled toselectively provide an LO signal to the mixer at either of those twofrequencies. In operation, the mixer circuit receives an RF signal fromthe RF amplifier and an LO signal from the multiple-frequency localoscillator and provides an IF signal to the IF amplifier. The input RFsignal is provided to the RF amplifier from, for example, a satelliteantenna or an optical cable.

In this device, because the multiple-frequency local oscillator canprovides an LO signal at one of a multiple of frequencies such as ateither 9.75 GHz or 10.6 GHz, the device is able to convert an input RFsignal covering both frequency bands 10.7-11.7 GHz and the 11.7-12.75GHz, and provides an output RF signal at a frequency between 950-1950MHz or 1100-2150 MHz. The input RF frequency range is thus greatlyimproved as compared with currently available single downconvertersystems.

In an alternative embodiment depicted in FIG. 11, the frequencyconversion further includes, in addition to a mixer circuit 905, RF andIF amplifiers 910 and 920, and a multi-frequency local oscillator 915, aphase splitter circuit 912. Located between the mixer circuit and theLO, the phase splitter circuit receives the output LO signal from the LOand converts it into two LO signals having opposite phase but the samefrequency before providing them to the mixer circuit. In thisembodiment, mixer circuit 905 is designed to operate with the twoopposed phased LO signals; the RF and If amplifiers re differentialamplifiers.

As it will be apparent to those skilled in the art, numerousmodifications may be made within the scope of the present invention,which is not intended to be limited except in accordance with thefollowing claims.

What is claimed is:
 1. A multiple-frequency local oscillator having aplurality of LO input ports for coupling to a plurality of resonators,respectively, each of said plurality of resonators having apredetermined resonant frequency, said local oscillator operating toprovide at an LO output port an output LO signal at any one of saidresonant frequencies, said local oscillator comprising:a plurality ofoscillator circuit means having input terminals connected to said LOinput ports for coupling to said resonators, respectively, and outputterminals connected together to said LO output port, each oscillatorcircuit means being capable of operating with the resonator coupledthereto to provide an LO signal at the resonator's resonant frequency,said plurality of oscillator circuit means comprising two field effecttransistors (FETs), the gate terminals of the two FETs being coupled totwo resonators, respectively, the source terminals of the FETs beingconnected together and coupled to the ground potential via a sourceimpedance load, the drain terminals of the FETs being connected andcoupled to a DC power supply via two drain impedance loads,respectively, and a commonly shared impedance load; and means forcontrolling said plurality of oscillator circuit means such that onlyone of said oscillator circuit means is selected to operate while theother oscillator circuit means is prevented from operation, whereby saidoutput LO signal is at the frequency that is the resonant frequency ofthe resonator that is coupled to said selected oscillator means.
 2. Thelocal oscillator of claim 1 wherein said two FETs are depletion modeFETs, and said means for controlling said plurality of oscillatorcircuit means comprises means for applying a ground or a positivepotential to the gate of one of said FETs to turn it on and applying anegative potential to the gate of the other FET to turn it off.
 3. Thelocal oscillator of claim 1 wherein one of said resonators has aresonant frequency of approximately 9.75 GHz and the other resonator hasa resonant frequency of approximately 10.6 GHz.
 4. A multiple-frequencylocal oscillator having a plurality of LO input ports for coupling to aplurality of resonators, respectively, each of said plurality ofresonators having a predetermined resonant frequency, said localoscillator operating to provide at an LO output port an output LO signalat any one of said resonant frequencies, said local oscillatorcomprising:a plurality of oscillator circuit means having inputterminals connected to said LO input ports for coupling to saidresonators, respectively, and output terminals connected together tosaid LO output port, each oscillator circuit means being capable ofoperating with the resonator coupled thereto to provide an LO signal atthe resonator's resonant frequency, said plurality of oscillator circuitmeans comprising two field effect transistors (FETs), the gate terminalsof the two FETs being coupled to two resonators, respectively, thesource terminals of the FETs being coupled to the ground potential viatwo source impedance loads, respectively, the drain terminals of theFETs being connected to a DC power supply via two drain impedance loads,respectively, and a commonly shared impedance load; and means forcontrolling said plurality of oscillator circuit means such that onlyone of said oscillator circuit means is selected to operate while theother oscillator circuit means is prevented from operation, whereby saidoutput LO signal is at the frequency that is the resonant frequency ofthe resonator that is coupled to said selected oscillator means.
 5. Thelocal oscillator of claim 4 wherein said two FETs are depletion modeFETs, and said means for controlling said plurality of oscillatorcircuit means comprises means for applying a ground or a positivepotential to one of said FETs to turn it on and applying a negativepotential to the other FET to turn it off.
 6. The local oscillator ofclaim 4 wherein one of said resonators has a resonant frequency ofapproximately 9.75 GHz and the other resonator has a resonant frequencyof approximately 10.6 GHz.
 7. A frequency conversion device forconverting an input RF signal into an output IF signal comprising:amultiple-frequency local oscillator having a plurality of LO input portsfor coupling to a plurality of resonators, respectively, each of saidplurality of resonators having a predetermined resonant frequency, saidlocal oscillator operating to provide at an LO output port an output LOsignal at any one of said resonant frequencies. said multiple-frequencylocal oscillator comprising a plurality of oscillator circuit meanshaving input terminals connected to said LO input ports for coupling tosaid resonators, respectively, and output terminals connected togetherto said LO output port, each oscillator circuit means being capable ofoperating with the resonator coupled thereto to provide an LO outputsignal at the resonator's resonant frequency, and means for controllingsaid plurality of oscillator circuit means such that only one of saidoscillator circuit means is selected to operate while the otheroscillator circuit means are prevented from operation, whereby saidlocal oscillator provides an output LO signal at the frequency that isthe resonant frequency of the resonator that is coupled to said selectedoscillator means, said plurality of oscillator circuit means comprisingtwo field effect transistors (FETs), the gate terminals of the two FETsbeing coupled to two resonators, respectively, the source terminals ofthe FETs being connected together and coupled to the ground potentialvia a source impedance load, the drain terminals of the FETs beingconnected and coupled to a DC power supply via two drain impedanceloads, respectively, and a commonly shared impedance load; and a mixercircuit for receiving an RF signal and said output LO signal from saidlocal oscillator and for generating an IF signal by mixing said RF andLO signals.
 8. The frequency conversion device of claim 7 wherein saidtwo FETs are depletion mode FETs, and said means for controlling saidplurality of oscillator circuit means comprises means for applying aground or a positive potential to one of said FETs so as to turn it onand applying a negative potential to the other FET to turn it off. 9.The frequency conversion device of claim 7 wherein one of saidresonators has a resonant frequency of approximately 9.75 GHz and theother resonator provides a signal at a frequency of approximately 10.6GHz.
 10. A frequency conversion device for converting an input RF signalinto an output IF signal comprising:a multiple-frequency localoscillator having a plurality of LO input ports for coupling to aplurality of resonators, respectively, each of said plurality ofresonators having a predetermined resonant frequency, said localoscillator operating to provide at an LO output port an output LO signalat any one of said resonant frequencies, said local oscillatorcomprising a plurality of oscillator circuit means having inputterminals connected to said LO input ports for coupling to saidresonators, respectively, and output terminals connected together tosaid LO output port, each oscillator circuit means being capable ofoperating with the resonator coupled thereto to provide an LO signal atthe resonator's resonant frequency, said plurality of oscillator circuitmeans comprising two field effect transistors (FETs), the gate terminalsof the two FETs being coupled to two resonators, respectively, thesource terminals of the FETs being coupled to the ground potential viatwo independent source impedance loads, respectively, the drainterminals of the FETs being connected to a DC power supply via two drainimpedance loads, respectively, and a commonly shared impedance load; anda mixer circuit for receiving an RF signal and said output LO signalfrom said local oscillator and for generating an IF signal by mixingsaid RF and LO signals.
 11. The frequency conversion device of claim 10wherein said two FETs are depletion mode FETs, and said means forcontrolling said plurality of oscillator circuit mean comprises meansfor applying a ground or a positive potential to one of said FETsthereby turning it on and applying a negative potential to the other FETthereby turning it off.
 12. The frequency conversion device of claim 10wherein one of said resonators has a resonant frequency of approximately9.75 GHz and the other resonator has a frequency of approximately 10.6GHz.
 13. A multiple-frequency local oscillator having a plurality of LOinput ports for coupling to a plurality of resonators, respectively, andan LO output port, each of such plurality of resonators having aresonant frequency, said local oscillator operating to provide at the LOoutput port an LO output signal at any one of such resonant frequencies,said local oscillator comprising:a plurality of field effect transistors(FETs) coupled via their gate terminals to respective LO input ports forcoupling to respective resonators, the source terminals of the FETsbeing connected together and coupled to a low reference potential via acommon source impedance load, the drain terminals of the FETs beingconnected together to the LO output port and being coupled to a DC powersupply via a common drain impedance load; and means for controlling saidplurality of FETs such that only one of said FETs is selectively turnedon while the others are turned off, whereby such LO output signal is atthe resonant frequency of the resonator coupled to said selected FET.14. The local oscillator of claim 13 implemented as a semiconductorintegrated circuit or a portion thereof.
 15. The local oscillator ofclaim 13 implemented as a GaAs integrated circuit or a portion thereof.16. The local oscillator of claim 13 wherein said FETs are depletionmode FETs, and said means for controlling said plurality of FETscomprises means for applying a zero or positive voltage between the gateand source of said selected FET to turn it on and applying a negativevoltage between the gate and source of the other FETs to turn them off.17. The local oscillator of claim 13 comprising two FETs for coupling totwo resonators having respective resonant frequencies of approximately9.75 GHz and 10.6 GHz.
 18. A frequency conversion device for convertingan RF input signal to an IF output signal comprising:amultiple-frequency local oscillator having a plurality of LO input portsfor coupling to a plurality of resonators, respectively, and an LOoutput port, each of such plurality of resonators having a resonantfrequency, said local oscillator operating to provide at the LO outputport an LO output signal at any one of such resonant frequencies, saidlocal oscillator comprising a plurality of field effect transistors(FETs) coupled via their gate terminals to respective LO input ports forcoupling to respective resonators, the source terminals of the FETsbeing connected together and coupled to a low reference potential via acommon source impedance load, the drain terminals of the FETs beingconnected together to the LO output port and being coupled to a DC powersupply via a common drain impedance load, and means for controlling saidplurality of FETs such that only one of said FETs is selectively turnedon while the others are turned off, whereby such LO output signal is atthe resonant frequency of the resonator coupled to said selected FET;and a mixer circuit for receiving such RF input signal and such LOoutput signal from said local oscillator and generating such IF signalby mixing such signals.
 19. The frequency conversion device of claim 18implemented as a semiconductor integrated circuit.
 20. The frequencyconversion device of claim 19 implemented as a GaAs integrated circuit.21. The frequency conversion device of claim 18 wherein said FETs aredepletion mode FETs, and said means for controlling said plurality ofFETs comprises means for applying a zero or positive voltage between thegate and source of said selected FET to turn it on and applying anegative voltage between the gate and source of the other FETs to turnthem off.
 22. The frequency conversion device of claim 18 comprising twoFETs for coupling to two resonators having respective resonantfrequencies of approximately 9.75 GHz and 10.6 GHz.
 23. Amultiple-frequency local oscillator having a plurality of LO input portsfor coupling to a plurality of resonators, respectively, and an LOoutput port, each of such plurality of resonators having a resonantfrequency, said local oscillator operating to provide at the LO outputport an LO output signal at any one of such resonant frequencies, saidlocal oscillator comprising:a plurality of field effect transistors(FETs) coupled via their gate terminals to respective LO input ports forcoupling to respective resonators, each FET source terminal beingcoupled to a low reference potential via a source impedance load, thedrain terminals of the FETs being connected together and coupled to a DCpower supply via a common drain impedance load; and means forcontrolling said plurality of FETs such that only one of said FETs isselectively turned on while the other FETs are turned off, whereby suchoutput LO signal is at the resonant frequency of the resonator coupledto said selected FET.
 24. The local oscillator of claim 23 implementedas a semiconductor integrated circuit or a portion thereof.
 25. Thelocal oscillator of claim 23 implemented as a GaAs integrated circuit ora portion thereof.
 26. The local oscillator of claim 23 wherein saidFETs are depletion mode FETs, and said means for controlling saidplurality of FETs comprises means for applying a zero or positivevoltage between the gate and source of said selected FET to turn it onand applying a negative voltage between the gate and source of theothers to turn them off.
 27. The local oscillator of claim 23 comprisingtwo FETs for coupling to two resonators having respective resonantfrequencies of approximately 9.75 GHz and 10.6 GHz.
 28. A frequencyconversion device for converting an RF input signal to an IF outputsignal comprising:a multiple-frequency local oscillator having aplurality of LO input ports for coupling to a plurality of resonators,respectively, and an LO output port, each of such plurality ofresonators having a resonant frequency, said local oscillator operatingto provide at the LO output port an LO output signal at any one of suchresonant frequencies, said local oscillator comprising a plurality offield effect transistors (FETs) coupled via their gate terminals torespective LO input ports for coupling to respective resonators, eachFET source terminal being coupled to a low reference potential via asource impedance load, the drain terminals of the FETs being connectedtogether and coupled to a DC power supply via a common drain impedanceload, and means for controlling said plurality of FETs such that onlyone of said FETs is selectively turned on while the other FETs areturned off, whereby such output LO signal is at the resonant frequencyof the resonator coupled to said selected FET; and a mixer circuit forreceiving such RF input signal and such LO output signal from said localoscillator and generating such IF output signal by mixing such RF and LOsignals.
 29. The frequency conversion device of claim 28 implemented asa semiconductor integrated circuit.
 30. The frequency conversion deviceof claim 29 implemented as a GaAs integrated circuit.
 31. The frequencyconversion device of claim 28 wherein said FETs are depletion mode FETs,and said means for controlling said plurality of FETs comprises meansfor applying a zero or positive voltage between the gate and source ofsaid selected FET to turn it on and applying a negative voltage betweenthe gate and source of the others to turn them off.
 32. The frequencyconversion device of claim 28 comprising two FETs for coupling to tworesonators having respective resonant frequencies of approximately 9.75GHz and 10.6 GHz.
 33. A multiple-frequency local oscillator having aplurality of LO input ports for coupling to a plurality of resonators,respectively, and an LO output port, each of such plurality ofresonators having a resonant frequency, said local oscillator operatingto provide at the LO output port an LO output signal at any one of suchresonant frequencies, said local oscillator comprising:a plurality offield effect transistors (FETs) coupled via their source terminals torespective LO input ports for coupling to respective resonators, thedrain terminals of the FETs being connected together to the LO outputport and being coupled to a DC Power supply via a common drain impedanceload; and means for controlling said plurality of FETs such that onlyone of said FETs is selectively turned on while the others are turnedoff, whereby such LO output signal is at the resonant frequency of theresonator coupled to said selected FET.
 34. The local oscillator ofclaim 33 implemented as a semiconductor integrated circuit or a portionthereof.
 35. The local oscillator of claim 34 implemented as a GaAsintegrated circuit or a portion thereof.
 36. The local oscillator ofclaim 33 wherein said FETs are depletion mode FETs, and said means forcontrolling said plurality of FETs comprises means for applying a zeroor positive voltage between the gate and source of said selected FET toturn it on and applying a negative voltage between the gate and sourceof the others to turn them off.
 37. The local oscillator of claim 33comprising two FETs for coupling to two resonators having respectiveresonant frequencies of approximately 9.75 GHz and 10.6 GHz.
 38. Afrequency conversion device for converting an RF input signal into an IFoutput signal comprising:a multiple-frequency local oscillator having aplurality of LO input ports for coupling to a plurality of resonators,respectively, and an LO output port, each of such plurality ofresonators having a resonant frequency, said local oscillator operatingto provide at the LO output port an LO output signal at any one of suchresonant frequencies, said local oscillator comprising a plurality offield effect transistors (FETs) coupled via their source terminals torespective LO input ports for coupling to respective resonators, thedrain terminals of the FETs being connected together to the LO outputport and being coupled to a DC Power supply via a common drain impedanceload, and means for controlling said plurality of FETs such that onlyone of said FETs is selectively turned on while the others are turnedoff, whereby such LO output signal is at the resonant frequency of theresonator coupled to said selected FET; and a mixer circuit forreceiving such RF input signal and such LO output signal from said localoscillator and generating such IF output signal by mixing such RF and LOsignals.
 39. The frequency conversion device of claim 38 implemented asa semiconductor integrated circuit.
 40. The frequency conversion deviceof claim 39 implemented as a GaAs integrated circuit.
 41. The frequencyconversion device of claim 38 wherein said FETs are depletion mode FETs,and said means for controlling said plurality of FETs comprises meansfor applying a zero or positive voltage between the gate and source ofsaid selected FET to turn it on and applying a negative voltage betweenthe gate and source of the others to turn them off.
 42. The frequencyconversion device of claim 38 comprising two FETs for coupling to tworesonators having respective resonant frequencies of approximately 9.75GHz and 10.6 GHz.